The Obama administration is poised to remove an Iranian opposition group from the United States' list of terrorist groups, officials briefed on the talk told the Wall Street Journal, in a move sure to upset Tehran as nuclear talks between the countries intensify.

The exile organization, the Mujahedin-e Khalq, or MeK, was named a terrorist group 15 years ago for allegedly being involved in assassinating U.S. citizens before the 1979 Islamic revolution in Iran, but the group had pursued an aggressive lobbying effort in Washington to clear up its status.

Being on the list means MeK's assets inside the U.S. are frozen and it is blocked from fundraising.

Secretary of State Hillary Clinton has yet to make a final decision, senior U.S. officials told the Wall Street Journal on Monday, but they suggested the department is looking favorably on the request to remove MeK from the terrorism list if it continues to leave a former military base in Iraq where it has been living in exile.

MeK already has renounced terrorism, though residents of the encampment, known as Camp Ashraf, have feared retribution if they leave the camp and return to Iran. There are 1,200 left at the camp, down from about 3,000.

A decision by Clinton is expected within 60 days of the last of the group leaving Camp Ashraf. The U.S. is working with the United Nations to resettle members of the group in other countries.

Warnings by Israel that it may attack Iran's nuclear facilities eased after Iran and the six powers trying to persuade Iran to make nuclear concessions met last month and agreed there was enough common will for another round in Baghdad on May 23. But with the Jewish state saying it is determined to stop Iran before it develops the capacity to build nuclear weapons, failure at the Iraq talks could turn such threats into reality.

A senior U.N. nuclear agency official urged Iran on Monday to allow access to sites, people and documents it seeks in its probe of suspicions that Tehran conducted secret research into nuclear weapons development.

The appeal came as International Atomic Energy Agency officials renewed talks with Iranian envoys aimed at persuading Tehran to allow IAEA experts to visit a suspect site at the Parchin military complex.

The agency believes that site was used by Iran to test multipoint explosives of the type used to set off a nuclear charge. Iran denies such experiments and insists it has no plans to turn its civilian nuclear program to making weapons.

A computer-generated drawing obtained by The Associated Press from a country tracking Iran's nuclear program depicts a containment chamber that would be used for such work. The IAEA has not commented, but Olli Heinonen, who was the senior official in charge of the Iran file until he left the IAEA last year, says the drawing is "very similar" to a photo he has seen and identifies as that of the Iranian chamber, adding even the colors of the two images match.

IAEA Deputy Director General Herman Nackaerts said the agency was seeking Iran's cooperation, ahead of Monday's talks at Iran's mission to the IAEA and other Vienna-based U.N. organizations.

The talks ended at mid-afternoon with neither side commenting. They were set to resume Tuesday morning.

The Associated Press contributed to this report.